One might guess that one way to improve the efficiency of a jet engine would be to increase the speed at which exhaust gases are expelled from the engine. In fact, that turns out not to be the case. Aeronautical engineers have discovered that a larger mass of gas moving at a lower velocity produces greater thrust in the engine. The modification that was developed to produce this effect is called a turbojet. The major difference between a turbojet and a ramjet is that the former contains a compressor attached to a turbine. The compressor consists of several rows of metal blades attached to a central shaft. The shaft, in turn, is attached to a turbine at the rear of the compressor. When air enters the inlet of a turbojet engine, some of it is directed to the core of the engine where the compressor is located. The compressor reduces the volume of the air and sends it into the combustion chamber under high pressure.
The exhaust gases formed in the combustion chamber have two functions. In the first place, they exit the rear of the chamber, as in a ramjet, providing the engine with a forward thrust. At the same time, the gases pass over the blades of the turbine, causing it to spin on its axis. The spinning turbine operates the compressor at the front of the engine, making possible the continued compression of new incoming air. Unlike a piston-powered engine, which has power strokes and exhaust strokes, the turbojet engine described here operates continuously. It is not subject, therefore, to the kind of vibrations experienced with a piston-powered propeller airplane.